On the Estimation of Nonrandom Signal Coefficients from Jittered Samples

This paper examines the problem of estimating the parameters of a bandlimited signal from samples corrupted by random jitter (timing noise) and additive iid Gaussian noise, where the signal lies in the span of a finite basis. For the presented classical estimation problem, the Cramer-Rao lower bound (CRB) is computed, and an Expectation-Maximization (EM) algorithm approximating the maximum likelihood (ML) estimator is developed. Simulations are performed to study the convergence properties of the EM algorithm and compare the performance both against the CRB and a basic linear estimator. These simulations demonstrate that by post-processing the jittered samples with the proposed EM algorithm, greater jitter can be tolerated, potentially reducing on-chip ADC power consumption substantially.Comment: 11 pages, 8 figure

Best practice report – operation and maintenance requirements

Deliverable 3.6.3 from the MERiFIC Project A report prepared as part of the MERiFIC Project "Marine Energy in Far Peripheral and Island Communities"This report is a deliverable of MERiFIC Work Package 3.6: ‘Operation and Maintenance requirements’ and has been produced as a cross border collaboration between IFREMER and the University of Exeter. The report provides an overview of guidelines and recommendations for the management of O&M operations necessary for an optimal exploitation of Marine energy plants, with a focus on the specific areas of South West Cornwall, UK and Iroise sea, Brittany, France. An overview of the onshore infrastructures and ports possibly suitable for management of such O&M operations is also provided. Management of scheduled and unscheduled maintenance operations are discussed in their various aspects including site accessibility. It should be noted that this topic, including weather window assessment for operations is discussed in more details in the additional MERIFIC report D3.6.2: Best Practice for installation proceduresMERiFIC was selected under the European Cross-Border Cooperation Programme INTERREG IV A France (Channel) – England, co-funded by the ERDF

Modelling Organic Dairy Production Systems

In this study, a large number of organic dairy production strategies were compared in terms of physical and financial performance through the integrated use of computer simulation models and organic case study farm data. Production and financial data from three organic case study farms were used as a basis for the modelling process to ensure that the modelled systems were based on real sets of resources that might be available to a farmer. The case study farms were selected to represent a range of farming systems in terms of farm size, concentrate use and location. This paper describes the process used to model the farm systems: the integration of the three models used and the use of indicators to assess the modelled farm systems in terms of physical sustainability and financial performance

Undersampled Phase Retrieval with Outliers

We propose a general framework for reconstructing transform-sparse images from undersampled (squared)-magnitude data corrupted with outliers. This framework is implemented using a multi-layered approach, combining multiple initializations (to address the nonconvexity of the phase retrieval problem), repeated minimization of a convex majorizer (surrogate for a nonconvex objective function), and iterative optimization using the alternating directions method of multipliers. Exploiting the generality of this framework, we investigate using a Laplace measurement noise model better adapted to outliers present in the data than the conventional Gaussian noise model. Using simulations, we explore the sensitivity of the method to both the regularization and penalty parameters. We include 1D Monte Carlo and 2D image reconstruction comparisons with alternative phase retrieval algorithms. The results suggest the proposed method, with the Laplace noise model, both increases the likelihood of correct support recovery and reduces the mean squared error from measurements containing outliers. We also describe exciting extensions made possible by the generality of the proposed framework, including regularization using analysis-form sparsity priors that are incompatible with many existing approaches.Comment: 11 pages, 9 figure

The influence of load history on synthetic rope response

Although used for the station-keeping of offshore equipment for several decades, synthetic ropes have only recently been used for marine renewable energy (MRE) devices. The fundamental mooring load differences between these two applications necessitate the detailed quantification of mooring component performance. Of particular importance for lifecycle analysis, installation and maintenance operations is the evolution of synthetic component performance over time due to load history and fatigue mechanisms. Changes to the stiffness and damping properties of these materials will affect the global response of the device if the mooring system and device responses are closely coupled. To address these uncertainties, tension experiments have been conducted on Nylon parallel-stranded rope samples at IFREMER as part of a MERiFIC (Marine Energy in Far Peripheral and Island Communities) consortium. Measurements are reported from tests involving three new samples subjected to a mixed creep/relaxation and harmonic loading regime. Different initial bedding-in levels are used to investigate the influence of load history on the immediate quasi-static and dynamic properties of the rope. For the load regimes studied, it is found that the rope condition with respect to the load-strain characteristic has a strong influence on the performance of the line.The authors would like to acknowledge the support of the MERiFIC project partners. The project is funded by the European Regional Development Fund through the Interreg IV-A programme

Best practice report – mooring of floating marine renewable energy devices

MERiFIC is an EU project linking Cornwall and Finistère through the ERDF INTERREG IVa France (Manche) England programme. The project seeks to advance the adoption of marine energy in Cornwall and Finistère, with particular focus on the island communities of the Parc naturel marin d’Iroise and the Isles of Scilly. Project partners include Cornwall Council, University of Exeter, University of Plymouth and Cornwall Marine Network from the UK, and Conseil général du Finistère, Pôle Mer Bretagne, Technôpole Brest Iroise, IFREMER and Bretagne Développement Innovation from France.This report is a deliverable of MERiFIC Work Package 3: ‘Dynamic Behaviour of Marine Energy Devices’ involving the collaboration of IFREMER (Institut français de recherche pour l'exploitation de la mer) in France and the University of Exeter in the United Kingdom. It is anticipated that the International Electrotechnical Commission’s guidelines Marine energy - Wave, tidal and other water current converters - Part 10: The assessment of mooring system for marine energy converters (MECs) will be published by the end of 2013. Although there are several guidance documents in the literature regarding the mooring of marine renewable energy (MRE) devices, the IEC document is one of the first to be produced on this subject, with guidance also available in documents produced by Det Norske Veritas. This document is intended to provide a concise introduction to mooring systems for MRE devices with reference given to guidelines and standards which may be applicable to the design of moorings for marine renewable energy (MRE) devices. The document begins by setting the scene to give background on the fundamental differences between conventional offshore equipment and MRE devices. In Section 2 design considerations are introduced, including cost, geometry and the importance of conducting risk analysis. Section 3 then gives an overview of moored system numerical modelling. Key findings of the report are then summarised in Section 4.MERiFIC was selected under the European Cross-Border Cooperation Programme INTERREG IV A France (Channel) – England, co-funded by the ERDF